Silicon based solar cells typically include textured crystalline silicon. A textured crystalline surface may refer to tetragonal pyramids with random pyramid base size in the few micronmeter range, where the most desirable size for the pyramid base is 1-5 micronmeters (um). The crystalline silicon surface may become textured through application of a texture formulation. A texture formulation may include a mixture of an alkaline chemical, potassium hydroxide (KOH) and isopropyl alcohol (IPA). However, this texture formulation has limitations that prevent the uniform texture formation for efficient solar cells. For example, conventional texture formulations can produce flat, untextured regions or poorly textured regions on the textured surface of the crystalline silicon substrate. Additionally, it is difficult for the conventional texture formulations to control the sizes of the pyramids formed on the surface of the silicon substrate. This is disadvantageous to the operation of a solar cell as light trapping efficiency of the solar cell is not optimal when the pyramid texture is formed of many different sized pyramids and when there are flat untextured regions on the surface of the crystalline silicon substrate.
The use of IPA in the texture formulation provides a narrow process window as IPA has a relatively low boiling point of 82.4° C. A conventional texture formulation which includes KOH and IPA is typically used at a temperature of approximately 80° C. and thus may have a limited texture etch rate due to the low bath temperature that is limited by the low boiling point of IPA. Texture formulations with IPA have a composition which changes with time and may not provide consistent texturing. Furthermore, IPA has a low flashing point of 12° C. which makes IPA a fire hazard. Consequently, an improved texture formulation which provides a consistent textured region across a silicon surface which is not subject to the drawbacks associated with textured formulations which include IPA is desired.